Tiger shark
2008/9 Schools Wikipedia Selection. Related subjects: Insects, Reptiles and Fish
| Tiger shark Fossil range: 56–0 MaEarly Eocene to Present |
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| Conservation status | ||||||||||||||||
 Near Threatened ( IUCN 2.3) |
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| Binomial name | ||||||||||||||||
| Galeocerdo cuvier Péron & Lesueur, 1822 |
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 Tiger shark range
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Squalus cuvier Peron and Lessueur, 1822 |
The tiger shark, Galeocerdo cuvier, the fourth largest predatory shark (after the great white shark, Greenland shark, and Pacific sleeper shark, is the only member of the genus Galeocerdo. Mature sharks average 3.25 to 4.25 m (11 to 14 ft) long and weigh 385 to 909 kg (850 to 2000 lb). It is found in many of the tropical and temperate regions of the world's oceans, and is especially common around islands in the central Pacific. This shark is a solitary hunter, usually hunting at night. Its name is derived from the dark stripes down its body, which fade as the shark matures.
The tiger shark is a predator, known for eating a wide range of items. Its usual diet consists of fish, seals, birds, smaller sharks, squid, and turtles. It has sometimes been found with man-made waste such as license plates or pieces of old tires in its digestive tract. It is notorious for attacks on swimmers, divers and surfers in Hawaii and is often referred to as "the wastebasket of the sea".
A tiger shark may be easily identified due to its dark stripes which are similar to a tiger pattern. It also has dorsal fins that are distinctively close to its tail. These sharks are often large in size and may encounter humans because they often visit shallow reefs, harbours and canals.
The tiger shark is second only to the great white shark, coming close with the bull shark in number of recorded attacks on humans and is considered, along with the great white, bull shark, and the oceanic whitetip shark to be one of the sharks most dangerous to humans. This may be due to its aggressive nature and frequency of human contact as it often inhabits populated waters such as Hawaiian beaches.
Taxonomy
The shark was first described by Peron and Lessueur in 1822 and was given the name Squalus cuvier. Müller and Henle, in 1837 renamed it Galeocerdo tigrinus. The genus, Galeocerdo, is derived from the Greek, galeos which means shark and the Latin cerdus which means the hard hairs of pigs. It is often colloquially called the man-eater shark.
The tiger shark is a member of the order Carcharhiniformes; members of this order are characterized by the presence of a nictitating membrane over the eyes, two dorsal fins, an anal fin, and five gill slits. It is the largest member of the Carcharhinidae family, commonly referred to as requiem sharks. This family includes some other well known sharks such as the blue shark, lemon shark and bull shark.
The largest tiger shark specimen was 7.3 m (24 ft) and is a contender for the largest carnivorous fish alongside the great white shark.
Distribution
The tiger shark is often found close to the coast, in mainly tropical and sub-tropical waters, though they can reside in temperate waters. Tiger sharks are the second largest predatory shark other than the great white. The shark's behaviour is primarily nomadic, but is guided by warmer currents, and it stays closer to the equator throughout the colder months. The shark tends to stay in deep waters that line reefs but does move into channels to pursue prey in shallower waters. In the western Pacific Ocean, the shark has been found as far north as Japan and as far south as New Zealand.
The shark has been recorded down to a depth just shy of 900 metres (3,000 ft) but is also known to move into shallow water - water that would normally be considered too shallow for a species of its size. It is also frequently found in river estuaries and harbors. At night it is usually found in shallow water.
Anatomy and appearance
Its skin can typically range from a blue to light green with a white or light yellow underbelly. The distinguishing dark spots and stripes are most outstanding in young sharks and fade as the shark matures. Tiger sharks regularly weigh 385 to 635 kg and are usually 3 m to 6 m long. The heaviest tiger shark recorded to date, was caught in Newcastle, NSW, Australia in 1954 and measured 7.3 m, scaled 1,524 kg. It has been estimated that the tiger shark can swim at a maximum speed of around 32 km/h, with short bursts of higher speeds that last only a few seconds.
The tiger shark's head is somewhat wedge-shaped, which makes it easy for the shark to turn quickly to one side. Tiger sharks, as with other sharks, have small pits on the side of their upper bodies which hold electrical sensors called the ampullae of lorenzini, enabling them to detect small muscle movements of other creatures, allowing them to hunt in darkness. In addition, the tiger shark, like many other sharks, has a reflective layer behind the retina called tapetum lucidum which allows light-sensing cells a second chance to capture photons of visible light, enhancing vision in low light condition. A tiger shark generally has long fins and a long upper tail; the long fins act like wings and provide lift as the shark maneuvers through water, whereas the long tail provides bursts of speed. A tiger shark normally swims using little movements of its body. Its high back and dorsal fin act as a pivot, allowing it to spin quickly on its axis.
Its teeth are highly specialized to slice through flesh, bone, and other tough substances such as the shells of sea turtles, and unusually among sharks, its upper and lower teeth have dissimilar shapes. Like most sharks, however, tiger shark teeth are continually replaced by rows of replacements from within its jaws.
Diet
The tiger shark, which generally hunts at night, has a reputation for eating anything it has access to, ignoring what nutritional value the prey may or may not hold. Apart from what is thought to be sporadic feeding, its most common foods include; common fish, squid, birds, seals, other sharks, and sea turtles. The shark has a number of features which make it a good hunter, such as excellent eyesight, which allows for access to murkier waters which can offer more varieties of prey and its acute sense of smell which enable it to react to faint traces of blood in its waters and is able to follow them to the source. The tiger shark's ability to pick up on low-frequency pressure waves produced by the movements of swimming animals, for example the thrashing of an injured animal, enables the shark to find a variety of prey.
The shark is known to be aggressive. The ability to pick up low-frequency pressure waves enables the shark to advance towards an animal with confidence, even in the environment of murky water where it is often found. The shark is known to circle its prey and even study it by prodding it with its snout. When attacking the shark devours all of its prey. Because of its aggressive nature of feeding, it is common to find a variety of foreign objects inside the digestive tract of a tiger shark. Some examples of more unusual items are automobile number plates, petroleum cans, tires, suits of armour, and baseballs. For this reason, the tiger shark is often regarded as the ocean's garbage can.
Reproduction
The tiger shark mates only once every 3 years. They breed by internal fertilization. It is the only species in its family that is ovoviviparous; its eggs hatch internally and the young are born live when fully developed. The male tiger shark will insert one of his claspers into the female's genital opening (cloaca), acting as a guide for the sperm to be introduced. The male uses its teeth to hold the female still during the procedure, often causing the female considerable discomfort. Mating in the northern hemisphere will generally take place between the months of March and May, with the young being born around April or June the following year. In the southern hemisphere, mating takes place in November, December, or early January.
The young are nourished inside the mother's body for up to 16 months, where the female can produce a litter ranging from 10 to 80 pups. A newborn tiger shark is generally 51 centimetres (20 in) to 76 centimetres (30 in) long and leaves its mother upon birth. It is unknown how long tiger sharks live, but it has been speculated to be 20 years.
Dangers and conservation
Although shark attacks on humans are a relatively rare phenomenon, the tiger shark is responsible for a large percentage of the fatal attacks that do occur on humans, and is regarded as one of the most dangerous species of sharks. Tiger sharks reside in temperate and tropical waters. They are often found in river estuaries and harbours, as well as shallow water close to shore, where they are bound to come into contact with humans. Tiger sharks are known to dwell in waters with runoff, such as where a river enters the ocean.
Tiger sharks have become a recurring problem in Hawaii and are considered the most dangerous shark species in Hawaiian waters. They are considered to be sacred 'aumakua' or ancestor spirits by the native Hawaiians, however between 1959 and 1976, 4,668 tiger sharks were hunted down in an effort to control what was proving to be detrimental to the tourism industry. Despite these numbers, little decrease was ever detected in the attacks on humans. It is illegal to feed sharks in Hawaii and any interaction with them such as cage diving is discouraged.
While the tiger shark is not directly commercially fished, it is caught for its fins, flesh, liver, which is a valuable source of vitamin A used in the production of vitamin oils, and distinct skin, as well as by big game fishers.
Trivia
- Known as " The Shark Arm case," in 1935, Australian gangster James Smith's arm was found in the stomach of a tiger shark. One of his crooked partners admitted to the crime, saying he killed James and hid him in a metal box, then cut the arm off because it wouldn't fit.
In popular culture
- In the first Jaws film, the first shark caught was a tiger shark.
- In 2007, Discovery Channel presented a special: Deadly Stripes: Tiger Sharks, for its annual Shark Week. During the show, South African shark scientist Mark Addison swam several times with a tiger shark he named "Dolores." The show contained footage of Addison hand-feeding the shark and even getting "rides" by holding onto the shark's dorsal fin for short periods of time. Addison claims that Dolores was able to recognize him on later trips to the same location.
- A tiger shark appeared in Deep Blue Sea as a bait for the mutant sharks.
- In The Spy Who Loved Me, The villain Jaws battles a juvenile tiger shark and ends the fight by giving the shark a fatal bite.
- The novel Life of Pi by Yann Martel features an appearance.
- The book A Pattern of Islands (1952) by Arthur Grimble describes accomplished Pacific islanders killing tiger sharks underwater in single combat, using only a knife.